Slewing drive technical

Slewing drives usually consist of an inner ring and an outer ring which are separated by balls with either an helical or true worm gear in the outer ring. This is mounted on a common housing that contains a worm shaft and shaft support bearings.

The rings may incorporate tapped or clearance holes for bolts. The rolling elements are usually separated by spacers and the raceways hardened and ground. Nitrile rubber strip seals retain lubricant in the bearing, and prevent the ingress of contaminants. Grease fittings allow re-lubrication to the bearing raceway, the worm gear and the supporting worm shaft bearings.

QCB Slewing Drives are normally supplied with motors in RIGHT HAND configuration as illustrated below.

Be aware the load speed is usually restricted to 3 rpm max. QCB Spur gear slew drives can offer faster load speeds.

1Enclosed housing9End cap O-rings
2Large O-ring10Outer oil seals
3Slewing ring11Taper roller bearing
4Top plate seal12Inner oil seals
5Upper positioning bolts13Worm shaft
6Top plate14Grease nipples
7Non-drive end cover15Lower positioning bolts
8End cap & bolts16Drive end adaptor cap

Slewing Drive Loads

Slewing drive can accommodate axial, radial and moment loads of any magnitude and in combination to provide either oscillatory movement or full rotation.

The loads and duty cycle of the machine must be properly defined so that an adequately sized, yet economical slewing drive can be selected - simply designing to maximum load is wasteful.

Download a copy of the Enquiry form from the DOWNLOADS page and submit it to QCB for assistance.

Transport, Storage & Mounting Preparation

As supplied, slewing drives are packed for storage in a dry (humidity < 75%), covered and vibration free store for a period not exceeding 12 months.

Slewing drives should only be transported and stored horizontally. Shock loads should be avoided to limit any damage to the raceways. Care must be taken not to dislodge seals or grease fittings during movement. Wooden or rubber spacers should be used to separate unwrapped bearings stacked vertically to avoid surface damage. If exposed, gear teeth should be protected from impact damage.

Light surface corrosion may occur in humid conditions but is easily removed from the external surfaces - it is more important that the raceways are well greased to remain rust free. QCB Slewing drives are epoxy coated at source in RAL 5005 Blue.

Either the standard threaded bolt holes or the lifting bolts provided should be used to lift the bearings in a flat plane. For safety check the weight of the ring to ensure any slings or chains used are suitable. Slewing rings should not be suspended from a crane by a single sling or placed on the ground vertically as they may deform under their own weight.

Flatness defects

Under load, flatness defects must not exceed the values tabulated to avoid tight spots or seizure, both of which will reduce the operating life of the ring. The values tabulated are for "long wave deviations" around the circumference. Note that X-roller bearings demand finer tolerances than ball bearings for smooth operation.

Shorter wave defects (e.g. between 2 bolt holes) must not exceed 1/4 of this value.

Defects in the radial direction (referred to as "conicity") must not exceed 0.05mm/m based on the raceway diameter.

Raceway Ø79121417192125
Flatness deviation in0.


QCB Slewing Drives can be used with Grade 10.9 or Grade 12.9 bolts.

The use of flat hardened washers is recommended to reduce surface pressures under the bolt head and nut. If cap screws are used, the specific pressure under the bolt head should not exceed the limits of the material. The use of any elastic spring or serrated washers is prohibited and their use will negate the warranty.

Untreated bolts should be lightly oiled and tightened progressively in steps of 60%, 80% and 100% bolt torque using a calibrated torque wrench, moving around the periphery of the slewing drive in approximately 120° steps. If the slewing drive is rotated during the tightening process any tight spots will become evident and should prompt immediate investigation.

Bolt torques should be checked before the machine enters service as a degree of "settling" may occur. Check again after 100 hours of operation and thereafter at least on an annual basis.

Recommended bolt torque figures are tabulated below.

Strength Class DIN/ISO 898Grade 10.9Grade 12.9
Yield point Rp 0.2940 MPa1100 Mpa
ISO Thread Stress x-section areaCore x-section areaTension forceTightening torqueTension forceTightening torque


QCB stock slewing drives are factory filled with a suitable grease. The regreasing interval is best determined by the environment

EnvironmentRecommended interval
Dry, clean workshop1000 hrs duty or 12 months
Outside, exposed500 hrs duty or 6 monthly
Aggressive50 hrs duty or 2 monthly

The amount of grease required is given in the following table:-

Raceway Ø3579121417192125
Worm gear356065100110110120130140150
Worm support brgs77710101010101010

During regreasing it is advisable to rotate the bearing to ensure even distribution of the lubricant.

The onus remains with the client to ensure the bearing is adequately and freshly lubricated at time of installation.

BrandGreaseOperating temp range
QCBYP 7014-1-20 to + 120 C
KluberIsoflex NBU 15-20 to +120 C
MOBILMobiltemp SHC 100-20 to + 120 C

WGR Rotation drives should be relubricated every 100 hours of operation (WGR 72 - 400 gr; WGR 110 - 1250 gr and WGR 114 1750 gr)

Tracking accuracy

The tracking accuracy of QCB Slewing Drives is catalogued. This is checked and recorded during assembly.

The input (worm shaft) is locked in place, the worm wheel (outer ring) can turn though the specified tracking angle.

Backlash calculation (1)

The backlash of QCB Slewing Drives is catalogued. The resultant angular movement of the worm shaft can be calculated.

With the worm wheel (outer ring) locked in place, the worm shaft can turn though the specified tracking angle x reduction ratio.

e.g. WGSE 21 125 25 H R tracking accuracy <0.15°; backlash < 0.15°x 125 = 18.75°

Backlash calculation (2)

The backlash of QCB Slewing Drives can be measured in terms of axial displacement of the worm shaft.

With the worm wheel (outer ring) locked in place, the worm shaft can move axially by 1/2 x Gear PCD(mm) x Tan (tracking precision angle).

e.g. WGSE 21 125 25 H R tracking accuracy <0.15°; gear pcd = 618.117mm; axial movement < (618.117/2) tan(0.15°) = 0.809mm which can only practically be measured in a suitable workshop environment




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